In nuclear medical imaging, a patient is injected with radiopharmaceutical material that dilutes and/or concentrates in the various body tissues. Gamma radiation emissions are collected from the patient utilizing gamma ray detectors, for example, gamma camera heads. These collected emissions are used to reconstruct a three dimensional image of the distribution of gamma ray sources within the patient.
Most reconstruction methods utilize filtered back projection. However, in some instances, for example, where the data is incomplete, iterative methods are used.
In some such iterative systems, a reconstruction cylinder containing the patient is defined. The intensity values are initially set to some single value over the entire cylinder and the iterative process then proceeds to correct the values based on the projection values acquired in the data collection process. Many variations of such processes are known.
The general idea of using body outline information in performing iterative reconstruction in nuclear medical imaging is known. U.S. Pat. No. 5,739,539, the disclosure of which is incorporated herein by reference, describes a method in which only regions within the body contour take part in the iterative reconstruction process. Namely, regions inside the body are set to a single non-zero value and regions outside the body are set to an initial zero value. At each iteration step, any non-zero pixels outside the body contour are also set to zero, before performing the next iteration.
In some systems, an attenuation map of the patient is obtained, to correct the image for attenuation of the gamma rays before they reach the detectors. This data may be used to determine the body contour in the prior art. Systems that determine body attenuation are described, for example, in PCT application no. PCT/IL99/00300; “Gamma Camera and CT System”, published as WO 00/75691, the disclosure of which is incorporated herein by reference.